Theoretical and experimental analysis of the dielectric properties of 3D orthogonal woven GFRP composites in the terahertz frequency range

A novel method to calculate the dielectric constant (epsilon(r)& PRIME;) of three-dimensional orthogonal woven glass fiber-reinforced polymer-matrix (3DOW-GFRP) composites in the terahertz (THz) frequency range is developed and experimentally verified using the THz time-domain spectroscopy (THz-TDS). The dielectric anisotropy is demonstrated through simulation by considering a single propagation direction of the THz waves and three different fiber orientations in unidirectional GFRP composites. Simulation results are compared to those obtained from the classic rule-of mixture equations to determine the representative equations for the three different cases of fiber orientations in the (x,y,z)-coordinate system and a new model is developed to calculate epsilon(r)& PRIME; of 3DOW-GFRP composites based on electromagnetic modeling principles. As opposed to previously reported lumped circuit models, our model addresses the issue of orthogonality of fiber and considers the shape and spatial disposition of the composite with respect to the polarization direction of the THz waves for accurate determination of epsilon(r)& PRIME;. A comparison between the measured and calculated epsilon(r)& PRIME; indicates that the proposed method is highly accurate with & LE; 2.68% maximum error, while the latter reaches 7.82% for the classic rule-of-mixture equations. This method is potentially useful for the design of 3DOW-GFRP with desired epsilon(r)& PRIME; for applications such as electromagnetic shielding and electrostatic discharging structures.